Is this your tv: https://www.which.co.uk/reviews/televisions/samsung-ue28j4100
If so it's native resolution is 1366x768, windows is correct. Your PS4 must be doing some kind of upscaling if it reports it's running at 1920x1080.
Thanks. You're right, I hadn't thought to look up specs for the tv.
Well, I'll invest in a new monitor at some stage.